This disclosure relates to polyester compositions and articles made therefrom. In particular, insert-molded articles having excellent heat cycle resistance can be obtained by insert molding of the polyester compositions with a metal insert.
Thermoplastic polyester compositions, such as poly(alkylene terephthalates), have valuable characteristics including mechanical strength, toughness, high gloss, and solvent resistance. Polyesters, therefore, have utility as materials for a wide range of applications, from automotive parts to electrical and electronic appliances. Automotive applications include metal-insert molded articles in which the metal inserts are placed inside of plastics. Such applications, however, usually require high durability even when subjected to a strenuous thermal cycle, for example, in an environment ranging from below 0° C. to over 100° C.
In particular, polyalkylene terephthalate compositions including glass reinforcing fibers have been used in insert-molded articles in which a metal part is embedded in a resin composition in order to take advantage of the properties of both the resin composition and the metal. Metal inserts have included, for example, aluminum, copper, iron, and brass. A continuing problem in obtaining such insert-molded articles, however, has been that they can still suffer from cracking when subjected, during use, to extreme temperature change, since the expansion and shrinkage coefficient (so-called liner expansion coefficient) can differ widely between the resin and metal portions of the insert-molded article.
Insert-molded articles have been applied in a wide variety of fields, including automobile parts and electrical or electronic parts. In particular, important applications of insert molding have been occurring in the automotive industry for use in making automotive parts located near an engine, the environment of which can greatly increase the need for heat cycle resistance. For example, insert-molded articles have been considered for use in parts of the automotive ignition system and distributor. Such insert-molded articles, however, can require even higher heat cycle resistant capabilities than previous applications. This challenge is increased by the fact that such insert-molded articles can have complicated structures, for examples, in which the thickness or shape of the resin composition can vary considerably in the article. Such complicated structures are especially prone to cracking. Therefore, uses and shapes of insert-molded articles have been undesirably limited and there remains a need for insert-molded articles having improved resistance to increasingly rigorous thermal cycles.
U.S. Pat. No. 6,512,027 discloses a resin composition comprising polybutylene terephthalate, glass fibers, and an impact resistance agent that is an epoxy-functionalized olefinic elastomer such as a graft copolymer of ethylene-glycidyl methacrylate-methyl methacrylate (EGMA-g-MMA), epoxy-modified styrene-butadiene-styrene block copolymer (ESBS), and epoxy-modified styrene-butadiene-styrene block copolymer (ESBS), which resin composition is designed for heat cycle resistance in metal-inserted parts.
U.S. Pat. No. 6,346,320 discloses a polyester resin composite molded article having thermal shock resistance that comprises polybutylene terephthalate, an inorganic filler, and, as an impact modifier, a modified ethylenic copolymer produced by graft-polymerization of maleic anhydride or other carboxylic acid anhydride, which copolymer is in the form of dispersed particles. Comparative impact modifiers in U.S. Pat. No. 6,346,320 include ethylene-glycidyl methacrylate-methyl acrylate copolymer.
US 2010/0266857 discloses a resin composition comprising polybutylene terephthalate, glass fibers, and a styrenic thermoplastic elastomer such as SEBS and epoxy-functionalized SBS, which can improve heat cycle resistance of metal inserted molded parts.
In view of the above, there remains a strong need for resin compositions for insert-molded articles, comprising a metal insert, that can endure even more rigorous changes between higher temperatures and lower temperatures over a long period of time, namely resin compositions providing excellent heat cycle resistance, including heat shock resistance, which resin compositions can, at the same time, exhibit other desirable mechanical properties such as flexural strength.